Voltage controlled oscillators should have a stable operating frequency as long as the input voltage does not change, but often shift frequency with changes in the power supply voltage or the ambient temperature.
Various circuits have been proposed to avoid this problem, and one prior arrangement utilizing a switched capacitor relaxation oscillator is disclosed in my article entitled "A Voltage Controlled Switched Capacitor Relaxation Oscillator", IEEE Journal of Solid State Circuits, Vol. SC-16 No. 4, August 1981. However, such circuits are undesirable for many applications in view of the excess phase jitter. Other articles which relate to the general subject matter of this invention include the following:
1. Charge-Pump Phase-Lock Loops, by Floyd M. Gardner, IEEE Transactions on Communications, Vol. COM-28, No. 11, Nov. 1980, pages 1849-1858. PA1 2. Fully Integrated Analog Filters Using BipolarJFET Technology, by Khen-Sang Tan and Paul R. Gray, IEEE Journal of Solid State Circuits, Vol. SC-13, No. 6, Dec. 1978, pages 814-821. PA1 3. A CMOS Low-Distortion Switched Capacitor Oscillator with Instantaneous Start-up, by Roger P. Colbeck, IEEE Journal of Solid-State Circuits, Vol. SC-19, No. 6, Dec. 1984, pages 996-998. PA1 4. NMOS Phase Lock Loop, by H. Khorramabadi, Memorandum No. UCB/ERL M77/67, 8 Nov. 1977, Electronics Research Laboratory, College of Engineering, University of California Berkeley, pages 1-30. PA1 5. Design of Integrated Analog CMOS Circuits - A Multichannel Telemetry Transmitter, by Wolfgang Stinhagen and Walter L. Engle, IEEE Journal of Solid State Circuits, Vol. SC-13, No. 6, Dec. 1978, pages 799-805. PA1 6. High Frequency CMOS Continuous - Time Filters, by Haideh Khorramabadi and Paul R. Gray, IEEE Journal of Solid State Circuits, Vol. SC-19, Dec. 1984, pages 939-948. PA1 7. An MOS Phase Locked Loop for Telecommunications Applications, by Yusuf A. Hague and Vikram A. Saletore, IEEE CH 1742-6/81, pages 303-307. PA1 8. Switched-Capacitor Circuit Design, by Roubik Gregorian, Kenneth W. Martin and Gabor C. Temes, Proceedings of the IEEE, Vol. 71, No. 8, August 1983, pages 941-966.
Accordingly, a principal object of the present invention is to provide a voltage controlled oscillator which is stabilized against frequency shifts resulting, for example, from power supply or temperature variations.